The children were the first to get sick. They spent Thanksgiving with sore throats and chills and fevers. By the end of the long weekend, the adults who had gathered for the family's holiday meal in Phoenix were feeling flu symptoms, too.

"We were all together for Thanksgiving, and the little kids got sick, then the adults got sick," Stephanie Gonzalez told CBS News. "It traveled through our family. Everybody kind of got over it. Everybody was fine."

Everybody but Alani "Joie" Murrieta.

Feeling ill, the mother of two left work early Nov. 26, then trudged into Urgent Care the next day. Doctors prescribed Tamiflu and rest, but neither worked.

The next day was worse. She was coughing uncontrollably, first mucous, then blood.

"She looked worried. She told her mom she was having a hard time breathing," Gonzalez told the network.

Her flu had given way to pneumonia. She had trouble breathing, then slipped into unconsciousness. By Tuesday — two days after Murrieta started feeling ill — she was dead.

It was a swift-moving tragedy for her family and an anxiety-inducing anecdote for anyone who's felt a familiar throat tickle and wondered how soon is too soon to go to the doctor.

Experts' answers are simple: Flu is deadly and should be treated with healthy respect.

"I'm afraid [Murrieta's] story is entirely consistent with severe influenza with a young adult," said William Schaffner, a physician and infectious diseases specialist at Vanderbilt University Medical Center in Nashville. Schaffner has not personally examined Murrieta or her records.

He and his colleagues say flu season started early this year, and the dominant strain of the virus that has emerged is the H3N2. That's the same strain that pinballed around the world last flu season and wreaked havoc in Australia during the southern hemisphere's winter months.

According to the CDC, more than 6,000 people have tested positive for the flu so far this year, more than double the number of people infected at this time last year.

"The H3N2 strain tends to make for a more severe disease, particularly among older people and people with underlying illness," Schaffner said. "But it can affect any child or adult and literally make them gravely ill within 48 hours, to the point where they have to be in the hospital, in intensive care. This can and does happen."

For people suddenly stressed out about a sudden high temperature or dry cough, there is an easy and inexpensive way to prevent influenza: annual vaccinations.

Schaffner, a self-proclaimed proselytizer of the flu-shot gospel, told The Washington Post flu shots can cut the chance of infection in half. For vaccinated people who end up getting the flu, it typically makes the symptoms milder. Lastly, getting the shot decreases a person's chances of passing the flu on to other people, including vulnerable groups such as children and the elderly.

According to The Post's Samantha Schmidt, a recent study showed vaccinations significantly reduced a child's chances of dying from the flu.

"Every year CDC receives reports of children who died from the flu. This study tells us that we can prevent more of these deaths by vaccinating more," Brendan Flannery, PhD, lead author and epidemiologist in the Influenza Division, said in a CDC statement.

Murrieta did not get a flu shot, her family told CBS News, but doctors say there's no way of knowing whether it would have made a difference for the 20-year-old.

For now, her family has started a GoFundMe page that has raised more than $18,000 of its $20,000 goal by Tuesday. They plan to use it to cover funeral expenses and provide for her two boys — the oldest is 2 years old, the younger 6 months.

"Our family is devastated that she is gone," the page said. " ... Alani left behind so many people that loved her."